Double covers of curves on Nikulin surfaces

We survey basic results concerning Prym varieties, the PrymBrill-Noether theory initiated by Welters, and Brill-Noether theory of general étale double covers of curves of genus g≥2. We then specialize to curves on Nikulin surfaces and show that étale double covers of curves on Nikulin surfaces of standard type do not satisfy Welters’ Theorem. On the other hand, by specialization to curves on Nikulin surfaces of non-standard type, we prove that general double covers of curves ramified at b=2, 4, 6 points are BrillNoether general; the case b=2 was already obtained by Bud [The birational geometry of Rg,2 and Prym-canonical divisorial strata, math.AG/01718.v2] with different techniques.